1. Field of the Invention
The present invention relates to screening machines utilizing rotating tumblers.
2. Description of the Prior Art
Machines that have tumblers are known in the art, for example, the present applicant's U.S. Pat. No. 4,167,975 shows a basic machine substantially similar in frame-work and rotating tumbler to that disclosed herein, but which does not include the refinements necessary for making it work for a dirt screening machine. U.S. Pat. No. 4,167,975 is a beach cleaning apparatus having a rotating drum for screening with a single brush in the interior of the drum for keeping the screen openings clean. Because sand is a free flowing material, the problems associated with screening are less than with dirt.
U.S. Pat. No. 3,825,018 also shows a machine using a rotating drum having a screen with a brush on the outside.